The present invention relates to gear motor drive assemblies, and more particularly to mounting means therefor.
Many present-day mechanisms require electric drives of the sort involving a relatively small motor and gear drive assembly, usually referred to as a gear motor. The gear motor is actually an integrated drive system, and in some applications is only required to provide a driven device with less than 360.degree. of rotational torque. For instance, drum switches and similar controlling and switching apparatus are operated by turning them back and forth through an arc of less than 360.degree.. Conventionally, a first switch is provided for starting the gear motion, and a limit switch or the like used to stop the gear motor so that the driven device is turned only to a predetermined point. However, simply deenergizing a motor will not cause it to stop, owing to the rotational inertia of the motor armature and drive elements. The motor will thus "overrun" past the turn-off position unless additional means are provided to positively stop rotation.
For this reason, it is conventional to provide a fixed stop adjacent a moving part of the drive or driven mechanism, and a coacting stop member on a movable part, such as the driven device or the drive shaft. Although the motor is deenergized before the movable stop reaches the fixed one, however, due to the overrunning tendency of the motor the stops eventually engage to provide a positive means for defining the travel of the shaft and associated driven mechanism. Unfortunately, the abrupt stop which occurs is highly detrimental to the motor and drive mechanism. In order to provide the necessary torque, the gear reduction unit is provided with a high mechanical advantage. Hence, the motor armature is spinning at a rapid rate when the mechanical stops engage. The gear drive mechanism is then forced to absorb the kinetic energy of the spinning armature, which frequently results in breakage of the drive mechanism.
In order to avoid this problem, it is conventional to provide a clutch between the motor and gear unit. The adjustment of the clutch slip is critical inasmuch as it must transfer a sudden application of torque, which occurs when the motor is first energized, in order to rapidly operate the driven mechanism. At the same time, the clutch must slip readily when the drive mechanism stops are engaged in order to absorb the kinetic energy of the still-moving rotor.
While considerable effort has been expended in the design and manufacture of such clutches their presence still adds an additional complication to the drive system, and moreover requires proper adjustment and maintenance. In addition, the presence of a clutch adds materially to the cost of the drive unit. For these reasons, it will be appreciated that it would be highly desirable to provide an improved, less expensive means for preventing breakage of the drive mechanism of a gear motor unit.
It is therefore an object of the present invention to provide an improved torque absorbing means for a gear motor unit.
Another object of the invention is to eliminate a clutch mechanism from a gear motor unit which utilizes positive mechanical stops to limit its travel.
Still another object is to provide an inexpensive torque absorbing means which is sufficiently compact to fit within conventionally sized gear motor support structures.